Outside of the process tools themselves, the chilled water plant is
typically the single largest consumer of electrical energy in a
semiconductor facility. This load includes not just chillers but also
cooling tower fans, primary pumps, secondary pumps and condenser pumps.
In order to meet the cooling requirements for any particular heat load,
many different combinations of this equipment can be run. However,
electricity consumption varies considerably depending on the
combination of equipment used and the operating levels of the
individual components. Selecting the optimal mix of equipment and
operating levels presents a substantial challenge for an automatic
control system and plant operators. Typically, no method is available
to predict the effect of interactions and variations in load demand and
outside air. This makes it challenging, if not impossible, to find an
equipment mix that achieves optimal energy use. In response to this
challenge, we set out to create a model/tool that would allow operators
to automatically determine the optimal equipment mix to satisfy cooling
requirements and minimize energy use. This paper describes how this
model was created and how it works.